This invention relates to drugs having either preventive or therapeutic effect on osteoarthritis and other diseases that involve the destruction and degeneration of the articular cartilage tissue.
Osteoarthritis involves the collapse of the articular cartilage surface and the resulting growth of new cartilage at the articular margins, joint deformity and loss of compliance, which are eventually manifested as the inflammation of the synovial membrane of the joint. Osteoarthritis is divided into two types, primary and secondary. Secondary osteoarthritis has predisposing causes such as trauma and infection that lead to the degeneration of cartilage but no predisposing cause can be identified in primary osteoarthritis. The principal lesion of osteoarthritis is the degeneration of articular cartilage and it may be attributable to the endogenous degeneration of articular cartilage and the mechanical stress on the joint; however, the mechanism of its etiology remains unknown in many aspects. Two major pathological phenomena occur in osteoarthritis. In one case, accelerated calcification of subchondral bone causes narrowing of joint fissures and destruction of the bone tissue (Bollet, A. J., Arthritis Rheum. 12, 152-163, 1969); in the other case, synovial inflammation causes either destruction or degeneration of the cartilaginous tissue (Huskisson, R. C. et al., Ann. Rheum. Dis. 38, 423-428, 1979; Campion, G. V. et al., Seimnars in Arthritis and Rheumatism 17, 232-245, 1988).
In inflammatory osteoarthritis, an observable decrease of proteoglycans (a matrix component of cartilaginous tissue) occurs due to such substances as IL-1 produced as from the synovial tissue (Tyler, J. A., Biochem. J. 225, 493-507, 1985); in addition, the production of proteoglycans by chondrocytes is suppressed (Ratcliffe, A., Biochem. J. 238, 571-580, 1986). As a result, the cartilage matrix would decrease (Pettipher, E. R. et al., Proc. Natl. Acad. Sci. USA 83, 8749-8753, 1986) to cause gradual loss of the articular cartilage layer.
The cartilage in the Joint tissue is classified as a permanent cartilage which is strictly distinguished from a grown cartilage which plays an important role in skeletal growth. Grown chondrocytes typically occurring in epiphysial cartilage plate go through the stages of growth, differentiation and calcification until they are replaced by bone, whereupon they fulfill their physiological function. In contrast, articular cartilage cells do not normally become calcified; this is because environmentally, calcification is strongly restrained from occurring in articular cartilage cells and because it is not calcified, the articular cartilage retains elasticity to thereby serve as a load-bearing cushion and assure high mobility at the joint. However, the elasticity of the articular cartilage surface is known to decrease in osteoarthritis (Myers, E. R. et al., Trans. Orthop. Res. USA 231, 1986). This is believed to be attributable to the rupturing of collagen fibers in the cartilaginous tissue (Stockwell, R. A. et al., J. Anat. 136, 425-439, 1982). The mechanism by which calcification is suppressed in the articular cartilage is not clear but calcification does take place when isolated articular cartilage cells are cultivated. Most probably, the strong suppressor of calcification of articular cartilage exists within the matrix surrounding the chondrocytes (Iwamoto, M. et al, J. Biol. Chem. 266, 461-467, 1991; Pacifici, M. et al., Exp. Cell Res. 192, 266-270, 1991).
Other differences can be found between the calcifying chondrocytes and the articular artilage cells. The calcifying cartilage hash alkaline phosphatase activity (Robinson, R., Biochem. J. 17, 286-293; 1923; Ali, S. Y., in xe2x80x9cCartilagexe2x80x9d (B. K. Hall, ed.), Vol. 1, pp. 343-378, Academic Press, New York) whereas only a hundredth of that activity is exhibited by the articular cartilage tissue (Iwamoto, M. et al., J. Biol. Chem. 266, 461-467, 1991). The cartilage matrix contains type X collagen and this occurs in a calcified cartilaginous tissue (Capasso, O. et al., Exp. Cell Res., 142, 197-206, 1982) but its occurrence is limited in the articular cartilage. It has been suggested that these markers are associated with the calcification of chondrocytes (Kato, Y. et al., Proc. Natl. Acad. Sci. USA 85, 9552-9556, 1988; Kwan, A. P. L. et al., J. Cell Biol. 109, 1849-1856, 1989). In osteoarthritis, articular cartilage cells have a higher alkaline phosphatase activity than normal articular cartilage cells (Mokondjimobe, E. et al., 39, 759-762, 1991) and it has been found in a study using human articular cartilage tissue that an osteoarthritic tissue has a higher alkaline phosphatase activity (Einhorn, T. A. et al., J. Orthop. Res. 3, 160-169, 1985). Similarly, the occurrence of type X collagen has been shown to be high in the cartilaginous tissue from patients with osteoarthritis (Hoyland, J. A. et al., Bone Miner. 15, 151-164, 1991). Based on these findings, it is speculated that the calcification of the cartilaginous tissue or subchondral bone in osteoarthritis is attributable to changes in the characters of articular cartilage cells, namely, the production of alkaline phosphatase and the occurrence of type X collagen.
The currently practised therapeutic regimens against osteoarthritis are no more than nosotropic or indirect as exemplified by preservative therapy, administration of anti-inflammatory agents or hyaluronic acid, and surgical treatments and there is no established therapeutic approach that may well be described as being xe2x80x9cetiotropicxe2x80x9d.
The purpose of the invention is to provide medicines which serve not only as preventives of osteoarthritis and other diseases that involve the destruction and degeneration of the articular cartilage tissue but also as etiotropic and direct therapeutics of such diseases.
Briefly, the present invention relates to preventives or therapeutics of diseases that involve the destruction and degeneration of the articular cartilage tissue, said preventives and therapeutics containing a PTH related peptide (PTHrP) or a PTHrP derived substance as an effective ingredient.
The parathyroid hormone related peptide (PTHrP) to be used in the invention embraces native PTHrP, PTHrP created by genetic engineering techniques and chemically synthesized PTHrP and may be exemplified by human, bovine and porcine PTHrP that are composed of 141 amino acids, with human PTHrP being preferred. The term xe2x80x9cPTHrP derived substancexe2x80x9d means partial peptides of the above-listed PTHrPs, as well as peptides that are obtained by partial modification of constituent amino acids of the PTHrP or partial peptides thereof through substitution, deletion or addition and which have the same activity. Examples of partial peptides of PTHrP include 1-34PTHrP, 1-84PTHrP, 3-141PTHrP, 7-141PTHrP, 35-141PTHrP, 85-141PTHrP, 107-141PTHrP, 107-140PTHrP, 1-87PTHrP, 3-87PTHrP, 7-87PTHrP, 1-111PTHrP, 3-111PTHrP and 7-111PTHrP, with human 1-34PTHrP and human 1-84PTHrP being preferred.
The 1-34PTHrP designates a partial peptide of PTHrP which is composed of 34 amino acids as counted from the N terminus of PTHrP. The number of amino acid residues to be substituted, deleted or added is not limited to any particular value as long as the activity intended by the present invention is retained. Diseases that involve the destruction and degeneration of the articular cartilage tissue include osteoarthritis and rheumatoid arthritis, with osteoarthritis being preferred.
As already mentioned, type X collagen and alkaline phosphatase are known to be critical substances that occur during calcification of cartilage or subchondral bone and suppressing the occurrence of type X collagen and the production of alkaline phosphatase is effective for the purpose of ameliorating osteoarthritis. Other findings on osteoarthritis are the lowering of the ability of articular cartilage cells to synthesize the matrix and the deformity of cartilaginous tissue by matrix decomposition; in view of this, a preferred therapeutic of osteoarthritis is a drug that does not interfere with but accelerate the synthesis of proteo-glycans which are a component of the cartilage matrix. Needless to say, the preferred drug should not cause any untoward effect on the growth and differentiation of chondrocytes such as by interfering with their growth.
The efficacy of the PTHrP in the invention against the diseases that involve the destruction and degeneration of the articular cartilage tissue can be verified by the following procedures.
The action on the growth of chondrocytes, the action on the occurrence of type X collagen which is a critical marker in the degeneration of cartilaginous tissue, alkaline phosphatase production and the ensuing calcification, as well as the action on the occurrence of type II collagen which is a cartilage matrix component can be verified by an experiment for cultivating grown chondrocytes of a young rabbit in a centrifugal tube (Kato, Y. et al., Proc. Natl. Acad. Sci. USA 85, 9552-9556, 1988; Iwamoto, M. et al., Develop. Biol. 136, 500-506, 1989) and by a system of plane cultivation of grown chondrocytes (Shimomura, Y. et al., Calcif. Tissue Res. 19, 179-187, 1975). Particularly in the case of cultivation in a centrifugal tube, cartilage cells grew and differentiated to become calcified in about 20 days (Kato, Y. et al., Proc. Natl. Sci. Acad. USA 85, 9552-9556, 1988). In addition, when articular cartilage cells were cultivated in a similar culture system, the development of high alkaline phosphatase activity was accompanied by calcification (Pacifici, M. et al., Exp. Cell Res. 192, 266-270, 1991). It is therefore understood that these cultivation systems are models useful experimental model in evaluating the efficacy of drugs against the development of abnormal characters by articular cartilage cells in osteoarthritis.
The action of PTHrP on the matrix of chondrocytes can be verified using the synthesis of cartilage matrix proteoglycans as a marker. An applicable experimental model is such that PTHrP is allowed to act on cultured chondrocytes during matrix synthesis, with the incorporation of 35S-sulfuric acid into the matrix being used as a marker.
In order to characterize the above-described actions of PTHrP, the presence of PTHrP receptors in chondrocytes must be verified. As a matter of fact, it has been shown that the presence of PTH receptors in chondrocytes is critical to the development of various actions of PTH on chondrocytes (Lee, K. et al., Endocrinology, 134, 441-450, 1994).